This invention relates to producing hydrocarbons from a hydrocarbon-containing subterranean formation employing a complexed polysaccharide.
Processes for the production of petroleum from a petroleum-containing subterranean formation employing an aqueous driving fluid containing a thickening agent are well known.
Oil accumulated within a subterranean formation can be recovered, or produced, through wells from the formation using the natural energy within the formation. However, producing operations deplete the natural energy relatively rapidly. Thus, a large amount of the oil is left in a subterranean formation if only the natural energy is used to produce the oil. This production by depletion of the natural energy is often referred to as primary production. Where natural formation energy is inadequate or has become depleted, supplementary operations, often referred to as secondary recovery operations, are used to improve the extent of recovery of the oil. In the most successful and most widely used supplemental recovery operations, a fluid is injected through an injection means, comprising one or more injection wells. The fluid is passed into the formation, displacing oil within and moving it through the formation. The oil is produced from production means, comprising one or more production wells, as the injected fluid passes from the injection means toward the production means. In a particular recovery operation of this sort, water is employed as the injected fluid, and the operation is referred to as waterflooding. The injected water is referred to as the flooding water as distinguished from the in-situ, or connate, water.
While conventional waterflooding is effective in obtaining additional oil from an oil-containing subterranean formation, it has a number of shortcomings. Foremost among these shortcomings is the tendency of flooding water to "finger" through an oil-containing formation and to bypass substantial portions thereof. By fingering is meant the developing of unstable bulges or stringers which advance toward and into the production means more rapidly than the remainder of the flooding water. Furthermore, the water does not normally displace as much oil in the portions of the formation which it contacts as it potentially is capable of doing.
It has been established that waterfloods perform less satisfactorily with viscous oils than with relatively non-viscous oils. The fingering and bypassing tendencies of the water are related to the ratio of the viscosity of the flooding water to that of the oil. The viscosities of different oils vary from as low as less than 1 or 2 centipoises to 1,000 centipoises or higher. Water has a viscosity of about 1 centipoise under atmospheric conditions.
Past suggestions for increasing the viscosity of flooding water have included incorporating water-soluble thickening additives in the water. Additives that have been suggested for this purpose include a wide variety of naturally occurring gums, sugars, and polymers. The bacterially produced heteropolysaccharides have been especially interesting as an additive for thickening flooding water. U.S. Pat. No. 3,020,207 discloses a process where the thickening agent is a heteropolysaccharide that has been reacted with an aldehyde, the heteropolysaccharide being a fermentation product produced by the action of bacteria of the genus Xanthomonas upon a carbohydrate. All patents referred to herein are incorporated in their entirety herein by reference. U.S. Pat. No. 3,352,358 discloses a process employing a thickened aqueous driving fluid where the thickening agent is polyvinyl alcohol sulfate. U.S. Pat. No. 3,372,749 discloses a process employing a thickened aqueous driving fluid wherein the thickening agent is a poly(glucosylglucan).
It is an object of this invention to improve the methods of recovering hydrocarbons from a hydrocarbon-containing subterranean formation by utilizing an improved thickened fluid in the drilling for said hydrocarbons or in any of the direct or indirect techniques for displacing hydrocarbons from said formation.
It is another object of this invention to provide a novel composition of matter.
It is yet another object to provide a novel aqueous liquid thickened with said composition of matter.
It is still another object to provide a process for preparing said compositions.